Functional OCT with parfocal retinal stimulation enables multi-site optoretinography under a single dark adaptation

Functional optical coherence tomography (OCT) enables depth-resolved imaging of stimulus-evoked intrinsic optical signal (IOS) changes in the retina, providing a noninvasive method for objective optoretinography (ORG) of retinal physiology. However, IOS imaging with raster-scan OCT is limited by long acquisition times, as each recording site typically requires a separate dark-adaptation cycle. To overcome this constraint, we developed a functional OCT system with parfocal retinal stimulation, in which the visible-light stimulus and near-infrared OCT imaging beams are co-registered at the retina. This configuration confines stimulation to a local retinal region with high spatial precision, preserves dark adaptation elsewhere, and enables multi-site IOS acquisition within a single adaptation cycle. Using visible-light flashes with variable bleaching levels (1-100%), we observed robust, spatially localized IOS confined to the stimulated regions of the retina. The IOS amplitude scaled linearly with bleaching level up to approximately 20% and exhibited saturation at higher intensities, consistent with the biophysical limits of phototransduction. This parfocal stimulation strategy establishes a scalable framework for spatially and depth-resolved functional retinal mapping, providing an objective optical analogue to microperimetry and a foundation for site-specific assessment of photoreceptor physiology.